The present invention relates to a communications system and method.
There is an increasing demand for high bandwidth communications systems which can carry data at rates which are significantly higher than those which are presently available to business or residential users. Systems which would benefit from very high data transfer rates include video-on-demand, video conferencing and video xe2x80x9ctelephonyxe2x80x9d, business and home Internet access, local area networks (LAN) interconnects, virtual private networks, teleworking, on-line games, high definition television, and many other applications demanding high information transfer rates.
In a conventional telephone communications system, the system operator""s main switched trunk network is connected to an access network which connects the trunk network to a subscriber""s individual telephone handset or private branch exchange (PBX). The access network is often known as the xe2x80x9clocal loopxe2x80x9d.
The vast majority of local loop networks in the United Kingdom and many other countries are based on wires which are either buried in the ground or are suspended overhead from poles. The wire extends from the regional access switch to the subscriber and is essentially dedicated to one subscriber and carries signals for no-one else.
Copper wire has conventionally been used primarily because of its relative low cost. However, copper wire can only carry data at a rate of about 2,400 to 9,600 bits per second (bps) without data compression. With more sophisticated techniques, this limit has been increased to about 57,000 bps. However, this is extremely slow when compared with the rate required for real-time video, which is in the region of 2 to 9 million bps (Mbps).
Some UK operators are now offering digital access services using the integrated services digital network (ISDN) system. However, the data transfer rate is still only about 64,000 to 128,000 bps and ISDN or ISDN2 and wired technology is still used. More recently, wired systems such as HDSL (high speed digital subscriber line) and ADSL (asymmetric digital subscriber line) can deliver up to 2,000,000 bps (2Mbps). However, as these are still wired systems, there is a very substantial start-up cost for any such system in that the operator must incur the significant cost of digging up roads, pavements, etc. to lay the cables or wires to a large number of subscribers before the system can begin operating. Indeed, the operator must take a large financial risk when setting up a new wired system in that the operator must lay a very large number of cables or wires before potential customers have committed themselves to the system so that the operator can offer a system which is already functional. This is obviously a significant risk, particularly where new technology is involved and the level of customer take-up of the system is unknown at the time the operator installs the infrastructure for the system.
Similarly, in a conventional, point-to-multipoint (broadcast) cellular system, each subscriber unit deals only with information intended for that subscriber.
Both the standard telephone system and cellular system mentioned above require some form of central station sending information to and receiving information from outlying or peripheral subscriber stations.
A wireless system is very much cheaper to install as no mechanical digging or laying of cables or wires is required. User sites can be installed and de-installed very quickly. Thus, radio communications systems have many attractive features in the area of large-scale system deployment. However, it is a feature of radio systems when a large bandwidth (data transfer rate) is required that, as the bandwidth which can be given to each user increases, it is necessary or the bandwidth of the radio signals to be similarly increased. Furthermore, the frequencies which can be used for radio transmission are closely regulated and it is a fact that only at microwave frequencies (i.e. in the gigahertz (GHz) region) or higher are such large bandwidths now available as the lower radio frequencies have already been allowed.
The problem with microwave or higher frequencies is that these radio frequencies are increasingly attenuated or completely blocked by obstructions such as buildings, vehicles, trees, etc. Such obstructions do not significantly attenuate signals in the megahertz (MHz) band but becomes a serious problem in the gigahertz (GHz) band. Thus, conventional wisdom has been that microwave or higher frequencies are difficult to use in a public access network which provides communication with a large number of distributed users.
The spectral efficiency of any wireless communications system is extremely important as there are many demands on radio bandwidth. As a matter of practice, the regulatory and licensing authorities are only able to license relatively narrow regions of the radio spectrum. A cellular system, which uses point-to-multipoint broadcasts, places high demands on the radio spectrum in order to provide users with a satisfactory bandwidth and is therefore not very efficient spectrally.
The use of repeaters or relays to pass on data from one station to another is well known in many applications. However, in each case, such repeaters broadcast signals, in a point-to-multipoint manner, and are therefore similar to a cellular approach and suffer from a corresponding lack of spectral efficiency.
According to a first aspect of the present invention, there is provided a communication system, the system comprising: a plurality of nodes, each node having: receiving means for receiving a signal transmitted by wireless transmitting means; transmitting means for wireless transmission of a signal; and, means for determining if a signal received by said node includes information for another node and causing a signal including said information to be transmitted by said transmitting means to another node if said received signal includes information for another node; each node having one or more substantially unidirectional point-to-point wireless transmission links, each of said links being to one other node only, at least some of the nodes being the origination and termination point of user traffic.
According to a second aspect of the present invention, there is provided a communications system, the system comprising: a plurality of nodes, each node having: receiving means for receiving a signal transmitted by wireless transmitting means; transmitting means for wireless transmission of a signal; and, means for determining if a signal received by said node includes information for another node and causing a signal including said information to be transmitted by said transmitting means to another node if said received signal includes information for another node; each node having one or more substantially unidirectional point-to-point wireless transmission links, each of said links being to one other node only, and being arranged such that transmission or reception of a signal at any particular frequency by the node takes place on only one link at a time.
According to a third aspect of the present invention, there is provided a communications system, the system comprising: a plurality of nodes, each node having: receiving means for receiving a signal transmitted by wireless transmitting means; transmitting means for wireless transmission of a signal; and, means for determining if a signal received by said node includes information for another node and causing a signal including said information to be transmitted by said transmitting means to another node if said received signal includes information for another node; each node having one or more substantially unidirectional point-to-point wireless transmission lines, each of said links being to one other node only, the links being arranged such that at least some of the nodes are not linked only to the nearest neighbour node(s).
Wireless transmission is used to provide communication with each node. In practice, each node is likely to be equipment associated with a user of or subscriber to the system. Each node is preferably stationary or fixed. The nodes operate in a peer-to-peer manner, which is in contrast to the central-master/peripheral-slave manner of say a cellular broadcast system. In the present invention, information is typically transferred in a series of xe2x80x9chopsxe2x80x9d from node to node around the system between a source node and a destination node. In the preferred embodiment, the nodes are logically connected to each other by plural point-to-point links between each linked pair of nodes and can be regarded as providing an interconnected xe2x80x9cwebxe2x80x9d covering a geographical area and providing a non-cellular network. The links are substantially unidirectional, i.e. signals are not broadcast but are instead directed to a particular node with signals being capable of being passed in both directions along the link.
It will be appreciated that some prior art systems have nodes which can communicate with each other with the nodes acting as simple repeaters. However, the individual transmissions in such prior art systems are often omnidirectional or use wide-angled transmission sectors and so such systems are still fundamentally cellular in structure. Such prior art systems thus tend to use point-to-multipoint transmissions, using a master/slave or central/peripheral architecture. In the preferred embodiment of the present invention, the nodes are connected in a peer-to-peer manner, with point-to-point links, in an interconnected mesh. In the present invention, many links across the system or network may be xe2x80x9cactivexe2x80x9d, that is carrying signals, at the same time so that plural pairs of linked nodes may be communicating with each other substantially simultaneously. In the preferred embodiment, for each node, only one link is xe2x80x9cactivexe2x80x9d at any one time and the link is active in only one direction at a time (i.e. a node is either transmitting only or receiving only on that link). In other words, if a node is transmitting or receiving on one of its links, it will not be receiving or transmitting on any of its other links. This greatly increases spectral efficiency compared to a cellular system or other systems using broadcast transmissions from a node. This configuration also helps to keep down the cost of the individual nodes as each node only requires one transmitter and one receiver.
Each node of the invention may be autonomous with respect to, for example, the transmission of signals to other nodes and need not be reliant on controls signals from some central controller or any other node. xe2x80x9cCallsxe2x80x9d between nodes can be effectively asynchronous and a call between a pair of nodes can start and finish effectively at any time, substantially independently of the state of any other call.
In an example of the invention, each node is a subscriber unit which can be mounted on or near a subscriber""s house. In addition, further nodes may be strategically placed in other suitable places according to the requirements of the operator. Thus, it is not necessary to provide metal (e.g. copper) wire, fibre optic or other fixed xe2x80x9chardxe2x80x9d links to each user, which saves the very high costs of digging up roads, laying fixed cables, etc. This means that the entry cost for a provider of the system can be relatively very low. A small system providing access for say a hundred or a thousand users can be set up very cheaply and additional users can be added later as demand grows.
In contrast to conventional point-to-multipoint broadcast radio systems, the present invention does not require a central transmitter with an extremely high bandwidth to service the subscribers"" data demands. In fact, except for possible interfacing to a trunk network, no high capital cost, high-profile, high-complexity sites are required for air-side interfacing, switching and transmission. These functions can be delocalised over the whole network in the system described herein. Moreover, the present invention does not require the large and unsightly radio masts/towers which are typical of cellular systems.
Nodes, as well as carrying traffic intended for other nodes, can also be the origination and termination point of users"" traffic. This has benefits for expansion of the network because, in principle, traffic can be injected and extracted from any node in the network, unlike cellular systems where a high-profile location (such as a hill top) has to be chosen for this purpose for example.
One or more nodes may be associated with plural users of or subscribers to the system. For example, a small business may have one node to which their internal LAN (local area network) is connected whereby all of the LAN users can access the communications system. A node with a bandwidth of say 2Mps could support up to 200 users each requiring a bandwidth of 9,600 bps.
Each node is used to pass on or xe2x80x9croutexe2x80x9d those signals which include information intended for other nodes in the system. If a node should fail in the system of the present invention, there is a loss of service only for the subscriber (if any) associated with that node and information for other nodes can be routed through nodes other than the failed node in the preferred embodiment.
Information is passed as necessary in a series of xe2x80x9chopsxe2x80x9d from one node to another via a preferably predetermined route until the information reaches its destination node.
The node are preferably linked so as to form plural transmission path loops thereby to provide plural choices of path for the transmission of a signal between at least some of the nodes. Each loop preferably consists of an even number of links. This allows for proper synchronisation of transmission and reception between nodes.
At least some of the nodes preferably have plural links to other nodes, each of said plural links between respective pairs of nodes being associated with a time slot. Each ink for each node may be associated with a distinct time slot. Thus, where TDM (time division multiplexing) is used, no node has more than one link having the same time slot number in the TDM frame structure.
The allocation of time slots to the links may be varied such that a link may selectively be associated with more than one time slot. This allows the effective bandwidth supported by a particular link to be increased, perhaps temporarily, as required by a user associated with a particular node for example.
According to a fourth aspect of the present invention, there is provided a communications system, the system comprising:
a plurality of nodes, each node having:
receiving means for receiving a signal transmitted by wireless transmitting means;
transmitting means for wireless transmission of a signal; and,
means for determining if a signal received by said node includes information for another node and causing a signal including said information to be transmitted by said transmitting means to another node if said received signal includes information for another node;
each node having a point-to-point link with at least one other node such that each node can transmit a signal to at least one other node, each link between respective pairs of nodes being associated with a distinct time slot, the nodes being linked so as to form transmission path loops thereby to provide plural choices of path for the transmission of a signal between at least some of the nodes, each loop consisting of an even number of links.
Each node of this aspect preferably has a direct line-of-sight link with at least one other node such that each node can transmit a signal to another node in line-of-sight with said each node. It will be understood that line-of-sight means that the path between two nodes connected by a line-of-sight link is entirely or substantially unobstructed such that the path is transparent or substantially transparent to the frequency used.
xe2x80x9cInformationxe2x80x9d in a signal may be for example software, whether for the operation of the node itself or for use by a subscriber associated with the node or otherwise, voice telephony data, video data, or telecommunications traffic generally.
Preferably, a signal including said information is transmitted by a node to another node if and only if a signal received at said node includes information for another node.
At least some of the nodes preferably have plural links to other nodes, each of said plural links between respective pairs of nodes being associated with a time slot.
In any of the aspects mentioned above, the number of nodes is preferably less than the number of links. This serves to ensure that there can be several distinct paths between any two nodes. Also, because the traffic equations are under-constrained, the traffic flowing on a link is not only a function of the subscriber injected/removed traffic, but also a function of the traffic on other links. This leads to a large number of possible traffic configurations for any given subscriber traffic. This means that (i) the point-to-point capacity of the network is increased relative to chain and tree topologies, (ii) it allows scope for network management strategies to alter traffic flows in parts of the network to prevent congestion without, in principle, adversely affecting the traffic carrying-capacity of the network as a whole, and (iii) the spectral efficiency of the system can be greatly improved over conventional cellular radio techniques.
In any of the aspects mentioned above, each node is preferably arranged to be in a transmission mode for a time period which alternates with a time period for a reception mode.
Other duplex techniques, such as Frequency Division Duplex (FDD), may be used.
Because each node is concerned with switching as well as the transmission of information traffic, the whole system can effectively behave as a distributed switch. This means that conventional access switches (i.e. exchanges), which represent significant capital expenditure, can be eliminated.
Many topologies for connecting the nodes are possible. Possible topologies include a fully interconnected topology, in which each node is directly connected to each other node; a linear chain topology, in which each node is connected to two other nodes in a chain; a tree topology, in which each node is connected to a predetermined number of other nodes such that there are no loops in the topological structure; a lattice topology, in which each node is connected to up to a predetermined number of nearest neighbours; and, a hypercube-type topology in which each node is linked to n other nodes. Non-regular topologies, with for example a random interconnection of nodes and/or a high degree of interconnectivity, are also possible and have many desirable properties. For example, a non-regular topology (like certain regular topologies) may provide a large number of possible routes for information to pass across the system or web 1. Combinations of topologies are also possible. For example, a hypercube structure of dimension n could service clusters of n fully interconnected n-valent nodes. A structure close to a perfect hypercube could alternatively be used for example.
It will be appreciated that in most areas where the system is deployed, the location of the nodes is dictated by the subscriber locations and that lines of sight between the nodes depends on the local geography. In such situations, it is unlikely that a prechosen network topology can be mapped onto the available lines of sight. A more pragmatic approach is to build up the network from the available lines of sight, carrying out the process with a view to creating a network with the desired traffic-bearing characteristics. Computer modelling has been carried out and it has been shown that it is possible to fulfil the requirements and preferred features of the network without having a regular form. The modelling indicates that structures worked up from the actual physical connectivity can perform well with regard to traffic-bearing properties.
Preferably, at least one node is arranged not to transmit to any other node information in a signal received by said at least one node when that information is addressed to said at least one node. Most preferably, all nodes operate in this manner.
Each node preferably has addressing means for adding to information in a received signal the address of a node to which a signal including said information is to be routed when said information is for another node. Thus, each node can easily pass on information intended for other nodes.
The addressing means may include means for determining the route of information through the system and adding an appropriate address to the information accordingly.
The nodes may have means for determining the route of information through the system as a whole.
Alternatively, the route of information through the system may be determined centrally by a central system controller. Thus, there may be provided a central system controller for determining the route of information through the system. The system may be used for passing control signals from the central system controller to each node.
At least one node may have means for determining if a received signal includes information for said at least one node and processing means for processing information in a signal addressed to said at least one node. All nodes may operate in this manner.
The transmitting means of the nodes preferably transmit signals at a frequency of at least about 1 GHz. A frequency greater than 2.4 GHz or 4 GHz may be used. Indeed, a frequency of 40 GHz, 60 GHz or even 200 GHz may be used. Beyond radio frequencies, other yet higher frequencies such as of the order of 100,000 GHz (infra-red) could be used. (The UK Wireless Telegraphy Act 1949 defines the upper frequency limit for the radio spectrum as 3xc3x971012 Hz.) The receiving means are arranged to receive signals at the frequencies transmitted by the transmitting means. It will be understood that, at least from a practical technical point of view, a greater bandwidth is more easily obtained if a higher frequency is used with suitable modulation.
The link between two nodes may be arranged to use simultaneously two or more frequency channels. This reduces the bandwidth load on a particular frequency channel.
The receiving and transmitting means may be arranged to transmit and detect circularly polarised radiation. The transmitting means preferably includes a highly directional transmitter. The receiving means preferably includes a highly directional receiver. Each of these preferred features helps to prevent interference between nodes and also helps to mitigate the effects of multipathing.
All nodes may be substantially identical. This simplifies the implementation of the present invention and helps to keep down costs.
The system can effectively be a self-contained network. On the other hand, by way of example, the system may be an access network connected to a conventional trunk network for providing access to subscribers or to other networks. A further node may be connected by a data connection to one of the nodes of the system and arranged to transfer a signal to or receive a signal from the trunk network or both.
One or more data storage servers can be connected to or provided at suitable nodes in the system. Various types of data can be stored on such data storage servers. For example, for so-called network computing, a user""s software applications can be stored at a data storage server remote from that subscriber""s node. The user accesses those applications through the system of the present invention. The applications can be easily updated by the software producer and can be used by plural subscribers two perhaps pay the software producer on a time-usage basis. The data stored on the data storage servers could be data for videos such as films (movies). This would not only provide a distributed video-on-demand service, but, in addition, from the system operator""s point of view, would allow video material to be distributed to the embedded servers using the same system possibly in a broadcast mode. In either case, frequently requested material migrates from main system libraries out to points in the system where it is required. This moderates the bandwidth requirements both for the video servers and for operator""s libraries.
Plural systems, each as described above, can be provided with each system being connected to at least one other system. The connection between such systems can be a radio connection, a wired connection such as a fibre optic link, or any other suitable means.
At least one link of a node may be arranged to use a first transmission frequency and at least one other link of said node may be arranged to use a second transmission frequency. This can be used to help prevent interference between nodes.
In an embodiment, some of the nodes are allocated to subscribers and some of the nodes are not allocated to subscribers, at least some of said non-allocated nodes being solely for carrying information traffic between subscriber nodes.
According to a fifth aspect of the present invention, there is provided a method of communications across a network of nodes, each node having one or more substantially unidirectional point-to-point wireless transmission links, each of said links being to one other node only, the method comprising the steps of:
(A) originating user data at a node;
(B) transmitting a signal including said user data from said node to another node along a substantially unidirectional point-to-point wireless transmission link between said nodes;
(C) receiving said signal at said other node;
(D) determining in said other node if the signal received by said other node includes information for a further node and transmitting a signal including said information from said other node to a further node along a substantially unidirectional point-to-point wireless transmission link between said nodes if said received signal includes information for a further node; and,
(E) repeating steps (B) to (D) until said user data reaches its destination node.
According to a sixth aspect of the present invention, there is provided a method of communications, the method comprising the steps of:
(A) transmitting a signal from one node to another node along a substantially unidirectional point-to-point wireless transmission link between said nodes;
(B) receiving said signal at said other node;
(C) determining in said other node if the signal received by said other node includes information for a further node and transmitting a signal including said information from said other node to a further node along a substantially unidirectional point-to-point wireless transmission link between said nodes if said signal includes information for a further node; and,
(D) repeating steps (A) to (C) until said signal reaches its destination node,
wherein transmission or reception of a signal at any particular frequency by a node takes place on only one link at a time.
According to a seventh aspect of the present invention, there is provided a method of communications, the method comprising the steps of:
(A) transmitting a signal from one node to another node along a substantially unidirectional point-to-point wireless transmission link between said nodes;
(B) receiving said signal at said other node;
(C) determining in said other node if the signal received by said other node includes information for a further node and transmitting a signal including said information from said other node to a further node along a substantially unidirectional point-to-point wireless transmission link between said nodes if said signal includes information for a further node; and,
(D) repeating steps (A) to (C) until said signal reaches its destination node,
the links being arranged such that at least some of the nodes are not linked only to the nearest neighbour node(s).
According to an eighth aspect of the present invention, there is provided a method of communications, the method comprising the steps of:
(A) transmitting a signal from one node to another node along a substantially unidirectional point-to-point wireless transmission link between said nodes;
(B) receiving said signal at said other node;
(C) determining in said other node if the signal received by said other node includes information for a further node and transmitting a signal including said information from said other node to a further node along a substantially unidirectional point-to-point wireless transmission link between said nodes if said signal includes information for a further node; and,
(D) repeating steps (A) to (C) until said signal reaches its destination node,
each link between respective pairs of nodes being associated with a distinct time slot, the nodes being linked so as to form transmission path loops thereby to provide plural choices of path for the transmission of a signal between at least some of the nodes, each loop consisting of an even number of links.
Preferably, at lest some of the nodes have plural links to other nodes, each of said plural links between respective pairs of nodes being associated with a time slot, and each transmission step on a link of said one node occurs during a distinct time slot and each receiving step on a link of said other node occurs during a distinct time slot.
Each node preferably adds to information in a received signal the address of a node to which a signal including said information is to be routed when said information is for another node.
Each node may have addressing means, the addressing means determining the route of the information through the system and adds an appropriate address to the information accordingly. Alternatively, a central system controller determines the route of information through the system.
The method preferably comprises the step of each node transmitting a signal including said information to another node if and only if a signal received at said node includes information for another node.
The method preferably includes the steps of determining in at least one node if a received signal includes information for said at least one node and processing the information in a signal addressed to said at least one node.
Preferably, the signals are transmitted at frequencies greater than about 1 GHz.
There may be at least two possible paths for transfer of data between a source node and a destination node. In such a case, the method may comprise the step of transmitting a copy of said data on each of said at least two paths. Alternatively, the method in such a case may comprise the steps of: transmitting from the source node a part only of said data on each of said at least two paths and reconstructing the data from said transmitted parts of said data in the destination node. This can increase the effective bandwidth of transmissions and allows redundancy to be achieved.
According to another aspect of the present invention, there is provided a telecommunications switching device, comprising a communications system as described above.